1. Field of the Invention
The present invention relates generally to a light curable dental liquid or paste, and more particularly to a dental liquid or paste which can be cured by irradiation of light to be utilized for teeth crown materials, denture base materials, dental cementing materials, dental bonding materials, dental filling materials, dental impression materials and caries-preventive materials.
2. Related Art Statement
Heat-polymerizable dental compositions wherein organic peroxides, such as benzoyl peroxide, are used as the polymerization initiators and cold-setting type dental compositions wherein Redox type polymerization initiators, such as a combination of benzoyl peroxide with a tertiary amine, are used as the polymerization initiators have been known in the art. Further known in the art is a composition containing a sensitizer such as benzoin alkyl ether to be cured by irradiation of ultraviolet rays.
However, the known heat-polymerizable and cold-setting type dental compositions have a disadvantage that the cured resins tend to contain air bubbles which lower the mechanical strength and water-proof properties, since they are prepared by mixing a powder with a liquid or kneading a paste with another paste. In addition, the heat-polymerizable dental compositions have another disadvantage that a complicated and time-consuming operation is required for polymerization. On the other hand, the cold-setting type dental compositions have additional disadvantages that the curing speed thereof is too high, which causes difficulties in clinical operation, and that the formed denture is colored, which deteriorates the appearance thereof, due to the undesirable action by the tertiary amine.
Compositions containing an ordinary light polymerization initiator sensitive to ultraviolet rays, such as benzoin alkyl ether, give rise to problems that the transmittance to ultraviolet rays effective for polymerization or curing is so low as to limit the depth of cured composition only to less than 2 mm, resulting in unsatisfactory curing depth, that a filter or other protection means is indispensable since the ultraviolet rays contain the rays having wavelengths of less than 320 nm which are harmful to human beings, and that the lifetime of a mercury lamp used as the irradiation source is short.
Further known in the art is a one-paste type dental composition containing a light polymerization initiator. Hawever, the known dental composition of this type has disadvantages that the mechanical strength, particularly the bending strength, of the cured product is low, and that it is inferior in ease of handling or operation when used in practical operation.